1. Field of Invention.
The present invention relates to a process using radiofrequency microwave energy to efficiently produce hydrogen from a source of hydrocarbons and oxygen with water.
2. Background.
Clean energy production is a noble task and fuel cells are one important ingredient. Yet fuel cells require a hydrogen-rich gas, and the subject invention has the potential to supply this by utilizing the high efficiency of microwave catalysis in reforming commonly available fuels, such as light hydrocarbons including alcohols, into cost effective hydrogen.
Microwaves are a form of quantum radiofrequency (RF) energy that is based upon the phenomenon of resonant interaction with matter of electromagnetic radiation in the microwave and RF regions since every atom or molecule can absorb, and thus radiate, electromagnetic waves of various wavelengths. The rotational and vibrational frequencies of the electrons represent the most important frequency range. The electromagnetic frequency spectrum is usually divided into ultrasonic, microwave, and optical regions. The microwave region is from 300 megahertz (MHz) to 300 gigahertz (GHz) and encompasses frequencies used for much communication equipment. For instance, refer to Cook, Microwave Principles and Systems, Prentice-Hall, 1986.
Often the term microwaves or microwave energy is applied to a broad range of radiofrequency energies particularly with respect to the common heating frequencies, 915 MHz and 2450 MHz. The former is often employed in industrial heating applications while the latter is the frequency of the common household microwave oven and therefore represents a good frequency to excite water molecules. In this writing the term xe2x80x9cmicrowavexe2x80x9d or xe2x80x9cmicrowavesxe2x80x9d is generally employed to represent xe2x80x9cradiofrequency energies selected from the range of about 500 to 5000 MHzxe2x80x9d, since in a practical sense this large range is employable for the subject invention.
The absorption of microwaves by the energy bands, particularly the vibrational energy levels, of atoms or molecules results in the thermal activation of the nonplasma material and the excitation of valence electrons. The nonplasma nature of these interactions is important for a separate and distinct form of heating employs plasma formed by arc conditions at a high temperature, often more than 3000xc2x0 F., and at much reduced pressures or vacuum conditions. For instance, refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Supplementary Volume, pages 599-608, Plasma Technology. In microwave technology, as applied in the subject invention, neither of these conditions is present and therefore no plasmas are formed.
Microwaves lower the effective activation energy required for desirable chemical reactions since they can act locally on a microscopic scale by exciting electrons of a group of specific atoms in contrast to normal global heating which raises the bulk temperature. Further this microscopic interaction is favored by polar molecules whose electrons become easily locally excited leading to high chemical activity; however, nonpolar molecules adjacent to such polar molecules are also affected but at a reduced extent. An example is the heating of polar water molecules in a common household microwave oven where the container is of nonpolar material, that is, microwave-passing, and stays relatively cool.
In this sense microwaves are often referred to as a form of catalysis when applied to chemical reaction rates. In this writing the term xe2x80x9cmicrowave catalysisxe2x80x9d refers to xe2x80x9cthe absorption of microwave energy by carbonaceous materials when a simultaneous surface chemical reaction is occurring.xe2x80x9d This gives rise to two slightly different forms of microwave catalysis. The first employs a carbonaceous material with a large internal pore surface to act as a chemical reaction surface. Activated carbon is a good example of this medium. The second form involves the use of conventional catalysts with carbonaceous material physically near this surface, and now the reaction occurs on the catalyst surface, while localized molecular energizing happens in close proximity. A good example of this is the use of silicon carbide either embedded in the catalyst substrate or alternately finely mixed with catalyst material. The subject invention employs both forms of microwave catalysis. For instance, refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume 15, pages 494-517, Microwave Technology.
Related United States patents include:
Referring to the above list, Wang et al. disclose conventional hydrogen production involving natural gas primary reforming and oxygen secondary reforming utilizing high temperatures above 1650xc2x0 F. No mention of microwave energy is made.
Cha et al.xe2x80x941 disclose a process for hydrogen production, employing radiofrequency energy with carbon black and hydrocarbon gases, particularly from mild gasification of coal. No oxygen is employed or suggested.
Cha et al.xe2x80x942, related to Cha et al.xe2x80x941, disclose a process for hydrogen production employing radiofrequency energy with char and a hydrogen-containing gas, such as water or hydrocarbons, particularly from mild gasification of coal. No oxygen is employed or suggested.
Cha discloses char-gas oxide reactions, such as NOx decomposition, and presents the background for efficient microwave catalysis usage for chemical reactions. The specification of this patent is hereby incorporated by reference.
The objectives of the present invention include overcoming the above-mentioned deficiencies in the prior art and providing a potentially economically efficient process for the microwave production of hydrogen-rich gas for potentially fuel cell usage.